package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.FileNotFoundException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.lucene.index.IndexFileNameFilter;
import org.apache.lucene.util.ThreadInterruptedException;

/**
 * A memory-resident {@link Directory} implementation.  Locking
 * implementation is by default the {@link SingleInstanceLockFactory}
 * but can be changed with {@link #setLockFactory}.
 */
public class RAMDirectory extends Directory implements Serializable {

    private static final long serialVersionUID = 1l;

    protected final Map<String, RAMFile> fileMap = new ConcurrentHashMap<String, RAMFile>();
    protected final AtomicLong sizeInBytes = new AtomicLong();

    // *****
    // Lock acquisition sequence:  RAMDirectory, then RAMFile
    // *****

    /** Constructs an empty {@link Directory}. */
    public RAMDirectory() {
        try {
            setLockFactory(new SingleInstanceLockFactory());
        } catch (IOException e) {
            // Cannot happen
        }
    }

    /**
     * Creates a new <code>RAMDirectory</code> instance from a different
     * <code>Directory</code> implementation.  This can be used to load
     * a disk-based index into memory.
     * <P>
     * This should be used only with indices that can fit into memory.
     * <P>
     * Note that the resulting <code>RAMDirectory</code> instance is fully
     * independent from the original <code>Directory</code> (it is a
     * complete copy).  Any subsequent changes to the
     * original <code>Directory</code> will not be visible in the
     * <code>RAMDirectory</code> instance.
     *
     * @param dir a <code>Directory</code> value
     * @exception IOException if an error occurs
     */
    public RAMDirectory(Directory dir) throws IOException {
        this(dir, false);
    }

    private RAMDirectory(Directory dir, boolean closeDir) throws IOException {
        this();

        IndexFileNameFilter filter = IndexFileNameFilter.getFilter();
        for (String file : dir.listAll()) {
            if (filter.accept(null, file)) {
                dir.copy(this, file, file);
            }
        }
        if (closeDir) {
            dir.close();
        }
    }

    @Override
    public final String[] listAll() {
        ensureOpen();
        // NOTE: fileMap.keySet().toArray(new String[0]) is broken in non Sun JDKs,
        // and the code below is resilient to map changes during the array population.
        Set<String> fileNames = fileMap.keySet();
        List<String> names = new ArrayList<String>(fileNames.size());
        for (String name : fileNames)
            names.add(name);
        return names.toArray(new String[names.size()]);
    }

    /** Returns true iff the named file exists in this directory. */
    @Override
    public final boolean fileExists(String name) {
        ensureOpen();
        return fileMap.containsKey(name);
    }

    /** Returns the time the named file was last modified.
     * @throws IOException if the file does not exist
     */
    @Override
    public final long fileModified(String name) throws IOException {
        ensureOpen();
        RAMFile file = fileMap.get(name);
        if (file == null) {
            throw new FileNotFoundException(name);
        }
        return file.getLastModified();
    }

    /** Set the modified time of an existing file to now.
     * @throws IOException if the file does not exist
     *  @deprecated Lucene never uses this API; it will be
     *  removed in 4.0. */
    @Override
    @Deprecated
    public void touchFile(String name) throws IOException {
        ensureOpen();
        RAMFile file = fileMap.get(name);
        if (file == null) {
            throw new FileNotFoundException(name);
        }

        long ts2, ts1 = System.currentTimeMillis();
        do {
            try {
                Thread.sleep(0, 1);
            } catch (InterruptedException ie) {
                throw new ThreadInterruptedException(ie);
            }
            ts2 = System.currentTimeMillis();
        } while (ts1 == ts2);

        file.setLastModified(ts2);
    }

    /** Returns the length in bytes of a file in the directory.
     * @throws IOException if the file does not exist
     */
    @Override
    public final long fileLength(String name) throws IOException {
        ensureOpen();
        RAMFile file = fileMap.get(name);
        if (file == null) {
            throw new FileNotFoundException(name);
        }
        return file.getLength();
    }

    /**
     * Return total size in bytes of all files in this directory. This is
     * currently quantized to RAMOutputStream.BUFFER_SIZE.
     */
    public final long sizeInBytes() {
        ensureOpen();
        return sizeInBytes.get();
    }

    /** Removes an existing file in the directory.
     * @throws IOException if the file does not exist
     */
    @Override
    public void deleteFile(String name) throws IOException {
        ensureOpen();
        RAMFile file = fileMap.remove(name);
        if (file != null) {
            file.directory = null;
            sizeInBytes.addAndGet(-file.sizeInBytes);
        } else {
            throw new FileNotFoundException(name);
        }
    }

    /** Creates a new, empty file in the directory with the given name. Returns a stream writing this file. */
    @Override
    public IndexOutput createOutput(String name) throws IOException {
        ensureOpen();
        RAMFile file = newRAMFile();
        RAMFile existing = fileMap.remove(name);
        if (existing != null) {
            sizeInBytes.addAndGet(-existing.sizeInBytes);
            existing.directory = null;
        }
        fileMap.put(name, file);
        return new RAMOutputStream(file);
    }

    /**
     * Returns a new {@link RAMFile} for storing data. This method can be
     * overridden to return different {@link RAMFile} impls, that e.g. override
     * {@link RAMFile#newBuffer(int)}.
     */
    protected RAMFile newRAMFile() {
        return new RAMFile(this);
    }

    /** Returns a stream reading an existing file. */
    @Override
    public IndexInput openInput(String name) throws IOException {
        ensureOpen();
        RAMFile file = fileMap.get(name);
        if (file == null) {
            throw new FileNotFoundException(name);
        }
        return new RAMInputStream(name, file);
    }

    /** Closes the store to future operations, releasing associated memory. */
    @Override
    public void close() {
        isOpen = false;
        fileMap.clear();
    }
}
